1. Field of Invention
The present invention relates to pigments.
2. Description of the Related Art
Disazo pyrazolone pigments, including Pigment Orange 13, Pigment Orange 34, Pigment Red 37, Pigment Red 38, Pigment Red 41, and Pigment Red 42, represent a class of general purpose colorants. They are utilized in a relatively broad range of applications, including plastics, solvent-based inks, water-based inks, solvent-based paints and water-based paints. Those having Colour Index identifications comprise the aforementioned examples and are represented as follows: ##STR1## wherein in the following pigments the X, Y and Z groups are the following:
______________________________________ Orange 13 X = Cl, Y = CH.sub.3, Z = H Orange 34 X = Cl, Y = CH.sub.3, Z = CH.sub.3 Red 37 X = OCH.sub.3, Y = CH.sub.3, Z = CH.sub.3 Red 38 X = Cl, Y = COOC.sub.2 H.sub.5, Z = H Red 41 X = OCH.sub.3, Y = CH.sub.3, Z = H Red 42 X = OCH.sub.3, Y = COOC.sub.2 H.sub.5, Z = H ______________________________________
The prior art literature pertaining to the preparation of improved disazo pyrazolone pigments, though not extensive, does address the objective. Thus, U.S. Pat. No. 4,341,701 (Ciba Geigy) describes the preparation of improved pyrazolone pigments by using a two-stage coupling technique. The advantages cited include higher coloring power, purity, dispersability, and transparency in many applications, including plastics, oil-based printing inks, gravure inks and paints. U.S. Pat. No. 3,671,281 teaches that a pyrazolone red pigment can be improved by heating in the presence of aniline, and GB No. 2,009,210 describes certain amine treatments to increase opacity for use in paints. SU No. 1344767 describes an improved process for manufacture of Orange 13 by the use of specified surfactants in order to reduce the cost.